Mixer drum drive with variable displacement motor

ABSTRACT

A vehicle includes an engine, a drum, a drum drive system, and a control system coupled to the engine and the drum drive system. The drum drive system includes a pump and a motor. The pump is mechanically coupled to the engine and configured to pump a fluid through a hydraulic system. The pump has a variable pump displacement. The motor is fluidly coupled to the pump by the hydraulic system and positioned to drive the drum to agitate the drum contents. The motor has a variable motor displacement. The control system is configured to receive pressure data indicative of a pressure of the fluid within the hydraulic system, reduce the variable motor displacement in response to the pressure of the fluid being less than a threshold system pressure, and reduce a speed of the engine based on the reduction of the variable motor displacement.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/542,553, filed Aug. 8, 2017, which is incorporatedherein by reference in its entirety.

BACKGROUND

Concrete mixer vehicles are configured to receive, mix, and transportwet concrete or a combination of ingredients that when mixed form wetconcrete to a job site. Concrete mixing vehicles include a rotatablemixing drum that mixes the concrete disposed therein.

SUMMARY

One embodiment relates to a vehicle. The vehicle includes an engine, adrum configured to mix drum contents received therein, a drum drivesystem coupled to the drum and the engine, and a control system coupledto the engine and the drum drive system. The drum drive system includesa pump and a motor. The pump is mechanically coupled to the engine andconfigured to pump a fluid through a hydraulic system. The pump has avariable pump displacement. The motor is fluidly coupled to the pump bythe hydraulic system and positioned to drive the drum to agitate thedrum contents. The motor has a variable motor displacement. The controlsystem is configured to receive a target speed for the drum, receivepressure data indicative of a pressure of the fluid within the hydraulicsystem, reduce the variable motor displacement in response to thepressure of the fluid being less than a threshold system pressure, andreduce a speed of the engine based on the reduction of the variablemotor displacement, while maintaining the target speed for the drum.

Another embodiment relates to a method for controlling a drum drivesystem of a mixer vehicle. The method includes operating, by a controlsystem, an engine, a variable displacement motor, and a variabledisplacement pump to provide a target drum speed. The variabledisplacement pump is selectively mechanically coupled to the engine suchthat a pump speed of the variable displacement pump is based on anengine speed of the engine. The variable displacement motor is fluidlycoupled to the variable displacement pump such that a motor speed of thevariable displacement motor is based on a flow of a fluid received fromthe variable displacement pump. The variable displacement motor ispositioned to drive a mixing drum at the target drum speed. The methodfurther includes monitoring, by the control system, pressure dataacquired by a pressure sensor indicative of a pressure of the flow ofthe fluid. The method further includes, in response to the pressure ofthe flow of the fluid being below a threshold pressure and atransmission of the mixer vehicle being in neutral, and whilemaintaining the target drum speed of the mixing drum: (i) decreasing, bythe control system, the engine speed of the engine, which therebydecreases the pump speed of the variable displacement pump, (ii)increasing, by the control system, a pump displacement of the variabledisplacement pump, and (iii) decreasing, by the control system, a motordisplacement of the variable displacement motor.

Still another embodiment relates to a drum drive system for a mixervehicle. The drum drive system includes a variable displacement pump, avariable displacement motor, and a controller. The variable displacementpump is selectively mechanically couplable to an engine such that a pumpspeed of the variable displacement pump is based on an engine speed ofthe engine. The variable displacement motor is fluidly coupled to thevariable displacement pump such that a motor speed of the variabledisplacement motor is based on a flow of a fluid received from thevariable displacement pump. The variable displacement motor isconfigured to drive a mixing drum at a target drum speed. The controlleris configured to selectively control the engine, the variabledisplacement pump, and the variable displacement motor to provide thetarget drum speed. To provide the target drum speed, the controller isconfigured to: (i) initially operate the variable displacement motor ata maximum motor displacement and operate the variable displacement pumpat a pump displacement that provides the target drum speed withoutneeding to actively manipulate the engine speed, (ii) increase the pumpdisplacement and decrease a motor displacement without needing toactively manipulate the engine speed while still providing the targetdrum speed, and (iii) increase the engine speed in response to the pumpdisplacement reaching a maximum pump displacement and the motordisplacement reaching a minimum motor displacement if necessary tomaintain the target drum speed.

The invention is capable of other embodiments and of being carried outin various ways. Alternative exemplary embodiments relate to otherfeatures and combinations of features as may be recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is a side view of a concrete mixing truck with a drum assemblyand a control system, according to an exemplary embodiment;

FIG. 2 is a detailed side view of the drum assembly of the concretemixing truck of FIG. 1, according to an exemplary embodiment;

FIG. 3 is a schematic diagram of a drum drive system of the concretemixing truck of FIG. 1, according to an exemplary embodiment;

FIG. 4 is a power flow diagram for the concrete mixing truck of FIG. 1having a drum drive system that is selectively coupled to a transmissionwith a clutch, according to an exemplary embodiment;

FIG. 5 is a flow diagram of a method for controlling a drum drive systemhaving a variable displacement pump and a variable displacement motor,according to an exemplary embodiment;

FIG. 6 is a control strategy plot outlining (i) pump displacement versusdrum speed, (ii) motor displacement versus drum speed, and (iii) enginespeed versus drum speed, according to an exemplary embodiment; and

FIG. 7 is a conventional control strategy plot outlining pumpdisplacement versus drum speed, (b) motor displacement versus drumspeed, and (c) engine speed versus drum speed.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the presentapplication is not limited to the details or methodology set forth inthe description or illustrated in the figures. It should also beunderstood that the terminology is for the purpose of description onlyand should not be regarded as limiting.

According to an exemplary embodiment, a concrete mixing vehicle includesa drum assembly having a mixing drum, a drum drive system, and a drumcontrol system. The drum control system may be configured to control thedrum drive system to rotate the mixing drum at a target speed. Accordingto an exemplary embodiment, the drum drive system is a hydraulic drumdrive system having two degrees of freedom. By having a drum drivesystem with a second degree of freedom, the drum drive systemfacilitates optimizing, balancing, and synchronizing the speed, thetorque, and the load of critical components of the drum drive system.The drum drive system of the present disclosure may advantageouslyminimize energy consumption or waste, reduce noise and emissions, andoptimize component working life relative to a single degree of freedomdrum drive system. The two degree of freedom drum drive system thereforeprovides a system that delivers better fuel consumption, optimal systemlife, and friendlier working environment. While the drum drive system isdescribed herein as a drum drive system for a concrete mixer truck, thedrum drive system may be applied to any vehicles having similaraccessory drive configurations.

A drum drive system typically includes a hydrostatic drive thatfunctions as both the power source and the speed control device for drumdrives. Hydrostatic drives may offer fast response, can maintain precisespeed under varying loads, and allow continuously variable speed ratiocontrol. A basic hydrostatic drive is a complete closed loop hydrauliccircuit containing a pump and a motor. The pump of the hydrostatic driveis typically a reversible variable-displacement pump. The pump may becoupled to and driven by a power-take-off (“PTO”) shaft coupled to anengine of the vehicle. The motor is conventionally a fixed displacementmotor. The motor may be coupled to the drum through a ratio reductiongearbox, pulley system, or otherwise coupled thereto. The pump mayinclude a built-in device to adjust the pump displacement and flowdirection.

The drum assembly may be operable in multiple working modes. The drummay be operated through a wide speed range, from lower than 1revolution-per-minute (“rpm”) in a transportation mode (e.g., while thevehicle is moving, etc.) to above 18 rpm in a loading mode and/or amixing mode. While in a discharging mode, it may be desirable to havethe lowest possible drum speed to achieve accurate discharging. Themixing mode of the drum may require the hydrostatic drive to provide aspeed range over 20:1 (e.g., the highest speed of the drum divided bythe lowest speed of the drum, etc.). The max speed range of a standardhydrostatic pump is about 10:1 due to maximum pump displacement,pressure limit, and/or torque limit thereof. A fixed displacement motorhas a fixed speed and therefore the speed range thereof is fixed (e.g.,1:1, etc.) based on the pump output provided thereto. Therefore, theengine has to run over its full speed range (approximately 3:1) to meetapplication requirements for the mixing mode. In the loading mode and/orthe mixing mode, the engine speed will typically run at the high idle(up to maximum governed speed). In the discharging mode, the engine mayrun near the low idle or independent of drum operation if the vehicle isbeing driven.

The limited speed ratio range of a typical hydrostatic drive presentssevere drawbacks in concrete mixing. Mixer vehicle have engines that aresized mainly for acceleration and climbing the most severe uphill gradesat maximum load. In concrete mixing operations, the required power istypically about one third of the engine capacity. Running at high idleresults in poor fuel efficiency. Other than unnecessary fuelconsumption, more emissions, more noise, and reduced engine life are allbyproducts. Another issue is the accuracy of concrete discharging. Someapplications prefer slow and accurate discharging rate. The engine maythereby be run at low idle to provide a flow discharge rate of mixturefrom the drum. However, the engine torque capacity becomes very weak atlow idle and any load change causes engine speed fluctuations, whichnegatively affects the discharging accuracy.

According to an exemplary embodiment, the drum drive system of thepresent disclosure replaces the conventional fixed displacement motorwith a variable displacement motor. The variable displacement motor mayprovide a speed range of 3:1 or 4:1. The speed range of the drum drivesystem is a product of the pump speed range multiplied by the motorspeed range. With a fixed displacement motor, the speed range of thedrum drive system is the speed ratio of the variable pump, typicallyaround 10:1. The drum drive system with the variable displacement motormay have a speed range that reaches up to 30:1 or 40:1. The increasedspeed range of the drum drive system having a variable displacementmotor relative to a drum drive system having a fixed displacement motorfrees up boundary limits for the engine, the pump, and the motor.Advantageously, with the increased capacity of the drum drive system,the engine does not have to run at either high idle or low idle, butrather may operate at a speed that provides the most fuel efficiency andmost stable torque. Also, the pump and the motor do not have to go todisplacement extremes to meet the speed requirements of variousapplications, but can rather be modulated to the most efficient workingconditions. The drum drive system of the present disclosure may providea desirable maximum overall drive ratio relative to traditionalarrangements. The maximum overall drive ratio may be the ratio of theengine speed to the drum speed and may vary based on the maximum pumpdisplacement, the minimum motor displacement, and/or the gearbox ratio.The maximum overall drive ratio may be limited in conventional systemsto prevent drum over speed at elevated (e.g., the highest possible,etc.) engine speed. In conventional systems, the maximum overall driveratio may be 120:1 (e.g., an engine speed of 2,100 rpm may provide adrum speed of 18 rpm at full pump displacement, etc.). The motor of thepresent disclosure may have a 3:1-4:1 reduction (e.g., at 100% to 33-25%displacement, etc. 2) and facilitate providing an overall drive ratio of30:1-40:1. The motor of the present disclosure may facilitate providingmaximum drum speed at or near engine idle speed. In one embodiment,traditional engine idle speed variation is displaced by motordisplacement variation.

Since the early application of hydrostatic drives, manual pumpadjustment has been the main method of drum speed control. Adding thecontrol and adjustment of the variable displacement motor not onlydoubles the operator demands, it also introduces risks of over speedingthe motor, over speeding the drum, and over pressurizing the system. Itis beyond a capacity of a human operator and a traditional mixer vehiclecontrol system to control pump displacement, motor displacement, andengine speed at the same time and guarantee the pressures and speeds areall within target operating ranges. The drum control system of thepresent disclosure is more sophisticated relative to those oftraditional mixer vehicles (e.g., those having fixed-displacementmotors, etc.). The drum control system may be configured to control pumpdisplacement and motor displacement while continuously electronicallycontrolling the engine speed (e.g., when the concrete mixing vehicle isnot being driven, etc.). To facilitate such control, the drum controlsystem is configured to monitor the working pressure on both sides ofthe motor and the pump, motor speed (i.e., which is proportional to thedrum speed), engine speed, engine torque, and/or percent load. By way ofexample, when the operator specifies a desired drum speed, the drumcontrol system may be configured to regulate the engine speed, pumpdisplacement, and motor displacement. The drum control system may beconfigured to maintain the engine speed at the lowest required levelwhile controlling pump displacement and motor displacement to providethe required power demand to operate the drum at the desired drum speed.In other embodiments, engine speed is not varied. In still otherembodiments, the drum control system reduces the risk of system overpressure and/or drum over speed, improving fuel economy by using lowerengine speeds, in response to independently controlled pump displacementand/or flow and independently controlled engine speed. Such independentpump control may be facilitated by way of a manual cable control, amanual analog control, or a manual electronic control. Such independentdrum speed control may be facilitated by way of a PTO speed controller.

According to the exemplary embodiment shown in FIGS. 1-4, a vehicle,shown as concrete mixing truck 10, includes a drum assembly, shown asdrum assembly 100. According to an exemplary embodiment, the concretemixing truck 10 is configured as a rear-discharge concrete mixing truck.In other embodiments, the concrete mixing truck 10 is configured as afront-discharge concrete mixing truck. As shown in FIG. 1, the concretemixing truck 10 includes a chassis, shown as frame 12, and a cab, shownas cab 14, coupled to the frame 12 (e.g., at a front end thereof, etc.).The drum assembly 100 is coupled to the frame 12 and disposed behind thecab 14 (e.g., at a rear end thereof, etc.), according to the exemplaryembodiment shown in FIG. 1. In other embodiments, at least a portion ofthe drum assembly 100 extends in front of the cab 14. The cab 14 mayinclude various components to facilitate operation of the concretemixing truck 10 by an operator (e.g., a seat, a steering wheel,hydraulic controls, a user interface, switches, buttons, dials, etc.).

As shown in FIGS. 1, 3, and 4, the concrete mixing truck 10 includes aprime mover, shown as engine 16. As shown in FIG. 1, the engine 16 iscoupled to the frame 12 at a position beneath the cab 14. The engine 16may be configured to utilize one or more of a variety of fuels (e.g.,gasoline, diesel, bio-diesel, ethanol, natural gas, etc.), according tovarious exemplary embodiments. According to an alternative embodiment,the engine 16 additionally or alternatively includes one or moreelectric motors coupled to the frame 12 (e.g., a hybrid vehicle, anelectric vehicle, etc.). The electric motors may consume electricalpower from an on-board storage device (e.g., batteries,ultra-capacitors, etc.), from an on-board generator (e.g., an internalcombustion engine, etc.), and/or from an external power source (e.g.,overhead power lines, etc.) and provide power to systems of the concretemixing truck 10.

As shown in FIGS. 1 and 4, the concrete mixing truck 10 includes a powertransfer device, shown as transmission 18. In one embodiment, the engine16 produces mechanical power (e.g., due to a combustion reaction, etc.)that flows into the transmission 18. As shown in FIGS. 1 and 4, theconcrete mixing truck 10 includes a first drive system, shown as vehicledrive system 20, that is coupled to the transmission 18. The vehicledrive system 20 may include drive shafts, differentials, and othercomponents coupling the transmission 18 with a ground surface to movethe concrete mixing truck 10. As shown in FIG. 1, the concrete mixingtruck 10 includes a plurality of tractive elements, shown as wheels 22,that engage a ground surface to move the concrete mixing truck 10. Inone embodiment, at least a portion of the mechanical power produced bythe engine 16 flows through the transmission 18 and into the vehicledrive system 20 to power at least a portion of the wheels 22 (e.g.,front wheels, rear wheels, etc.). In one embodiment, energy (e.g.,mechanical energy, etc.) flows along a first power path defined from theengine 16, through the transmission 18, and to the vehicle drive system20.

As shown in FIGS. 1-3, the drum assembly 100 of the concrete mixingtruck 10 includes a drum, shown as mixing drum 102. The mixing drum 102is coupled to the frame 12 and disposed behind the cab 14 (e.g., at arear and/or middle of the frame 12, etc.). As shown in FIGS. 1-4, thedrum assembly 100 includes a second drive system, shown as drum drivesystem 120, that is coupled to the frame 12. As shown in FIGS. 1 and 2,the concrete mixing truck 10 includes a first support, shown as frontpedestal 106, and a second support, shown as rear pedestal 108.According to an exemplary embodiment, the front pedestal 106 and therear pedestal 108 cooperatively couple (e.g., attach, secure, etc.) themixing drum 102 to the frame 12 and facilitate rotation of the mixingdrum 102 relative to the frame 12. In an alternative embodiment, thedrum assembly 100 is configured as a stand-alone mixing drum that is notcoupled (e.g., fixed, attached, etc.) to a vehicle. In such anembodiment, the drum assembly 100 may be mounted to a stand-alone frame.The stand-alone frame may be a chassis including wheels that assist withthe positioning of the stand-alone mixing drum on a worksite. Such astand-alone mixing drum may also be detachably coupled to and/or capableof being loaded onto a vehicle such that the stand-alone mixing drum maybe transported by the vehicle.

As shown in FIGS. 1 and 2, the mixing drum 102 defines a central,longitudinal axis, shown as axis 104. According to an exemplaryembodiment, the drum drive system 120 is configured to selectivelyrotate the mixing drum 102 about the axis 104. As shown in FIGS. 1 and2, the axis 104 is angled relative to the frame 12 such that the axis104 intersects with the frame 12. According to an exemplary embodiment,the axis 104 is elevated from the frame 12 at an angle in the range offive degrees to twenty degrees. In other embodiments, the axis 104 iselevated by less than five degrees (e.g., four degrees, three degrees,etc.) or greater than twenty degrees (e.g., twenty-five degrees, thirtydegrees, etc.). In an alternative embodiment, the concrete mixing truck10 includes an actuator positioned to facilitate selectively adjustingthe axis 104 to a desired or target angle (e.g., manually in response toan operator input/command, automatically according to a control scheme,etc.).

As shown in FIGS. 1 and 2, the mixing drum 102 of the drum assembly 100includes an inlet, shown as hopper 110, and an outlet, shown as chute112. According to an exemplary embodiment, the mixing drum 102 isconfigured to receive a mixture, such as a concrete mixture (e.g.,cementitious material, aggregate, sand, etc.), with the hopper 110. Asshown in FIGS. 1 and 2, the mixing drum 102 includes a port, shown asinjection port 130. The injection port 130 may provide access into theinterior of the mixing drum 102 to inject water and/or chemicals (e.g.,air entrainers, water reducers, set retarders, set accelerators,superplasticizers, corrosion inhibitors, coloring, calcium chloride,minerals, and/or other concrete additives, etc.). According to anexemplary embodiment, the injection port 130 includes an injection valvethat facilitates injecting the water and/or the chemicals from a fluidreservoir (e.g., a water tank, etc.) into the mixing drum 102 tointeract with the mixture, while preventing the mixture within themixing drum 102 from exiting the mixing drum 102 through the injectionport 130. In some embodiments, the mixing drum 102 includes multipleinjection ports 130 (e.g., two injection ports, three injection ports,etc.) configured to facilitate independently injecting different waterand/or chemicals into the mixing drum 102. The mixing drum 102 mayinclude a mixing element (e.g., fins, etc.) positioned within theinterior thereof. The mixing element may be configured to (i) agitatethe contents of mixture within the mixing drum 102 when the mixing drum102 is rotated by the drum drive system 120 in a first direction (e.g.,counterclockwise, clockwise, etc.) and (ii) drive the mixture within themixing drum 102 out through the chute 112 when the mixing drum 102 isrotated by the drum drive system 120 in an opposing second direction(e.g., clockwise, counterclockwise, etc.).

As shown in FIGS. 2-4, the drum drive system 120 includes a pump, shownas pump 122; a reservoir, shown as fluid reservoir 124, fluidly coupledto the pump 122; and an actuator, shown as drum motor 126. As shown inFIGS. 3 and 4, the pump 122 and the drum motor 126 are fluidly coupled.According to an exemplary embodiment, the drum motor 126 is a hydraulicmotor, the fluid reservoir 124 is a hydraulic fluid reservoir, and thepump 122 is a hydraulic pump. The pump 122 may be configured to pumpfluid (e.g., hydraulic fluid, etc.) stored within the fluid reservoir124 to drive the drum motor 126.

According to an exemplary embodiment, the pump 122 is a variabledisplacement hydraulic pump (e.g., an axial piston pump, etc.) and has apump stroke that is variable. The pump 122 may be configured to providehydraulic fluid at a flow rate that varies based on the pump stroke(e.g., the greater the pump stroke, the greater the flow rate providedto the drum motor 126, etc.). The pressure of the hydraulic fluidprovided by the pump 122 may also increase in response to an increase inpump stroke (e.g., where pressure may be directly related to work load,higher flow may result in higher pressure, etc.). The pressure of thehydraulic fluid provided by the pump 122 may alternatively not increasein response to an increase in pump stroke (e.g., in instances wherethere is little or no work load, etc.). The pump 122 may include athrottling element (e.g., a swash plate, etc.). The pump stroke of thepump 122 may vary based on the orientation of the throttling element. Inone embodiment, the pump stroke of the pump 122 varies based on an angleof the throttling element (e.g., relative to an axis along which thepistons move within the axial piston pump, etc.). By way of example, thepump stroke may be zero where the angle of the throttling element equalto zero. The pump stroke may increase as the angle of the throttlingelement increases. According to an exemplary embodiment, the variablepump stroke of the pump 122 provides a variable speed range of up toabout 10:1. In other embodiments, the pump 122 is configured to providea different speed range (e.g., greater than 10:1, less than 10:1, etc.).

In one embodiment, the throttling element of the pump 122 is movablebetween a stroked position (e.g., a maximum stroke position, a partiallystroked position, etc.) and a destroked position (e.g., a minimum stokeposition, a partially destroked position, etc.). According to anexemplary embodiment, an actuator is coupled to the throttling elementof the pump 122. The actuator may be positioned to move the throttlingelement between the stroked position and the destroked position. In someembodiments, the pump 122 is configured to provide no flow, with thethrottling element in a non-stroked position, in a default condition(e.g., in response to not receiving a stroke command, etc.). Thethrottling element may be biased into the non-stroked position. In someembodiments, the drum control system 150 is configured to provide afirst command signal. In response to receiving the first command signal,the pump 122 (e.g., the throttling element by the actuator thereof,etc.) may be selectively reconfigured into a first stroke position(e.g., stroke in one direction, a destroked position, etc.). In someembodiments, the drum control system 150 is configured to additionallyor alternatively provide a second command signal. In response toreceiving the second command signal, the pump 122 (e.g., the throttlingelement by the actuator thereof, etc.) may be selectively reconfiguredinto a second stroke position (e.g., stroke in an opposing seconddirection, a stroked position, etc.). The pump stroke may be related tothe position of the throttling element and/or the actuator.

According to another exemplary embodiment, a valve is positioned tofacilitate movement of the throttling element between the strokedposition and the destroked position. In one embodiment, the valveincludes a resilient member (e.g., a spring, etc.) configured to biasthe throttling element in the destroked position (e.g., by biasingmovable elements of the valve into positions where a hydraulic circuitactuates the throttling element into the destroked positions, etc.).Pressure from fluid flowing through the pump 122 may overcome theresilient member to actuate the throttling element into the strokedposition (e.g., by actuating movable elements of the valve intopositions where a hydraulic circuit actuates the throttling element intothe stroked position, etc.).

As shown in FIG. 4, the concrete mixing truck 10 includes a powertakeoff unit, shown as power takeoff unit 32, that is coupled to thetransmission 18. In another embodiment, the power takeoff unit 32 iscoupled directly to the engine 16. In one embodiment, the transmission18 and the power takeoff unit 32 include mating gears that are inmeshing engagement. A portion of the energy provided to the transmission18 flows through the mating gears and into the power takeoff unit 32,according to an exemplary embodiment. In one embodiment, the matinggears have the same effective diameter. In other embodiments, at leastone of the mating gears has a larger diameter, thereby providing a gearreduction or a torque multiplication and increasing or decreasing thegear speed.

As shown in FIG. 4, the power takeoff unit 32 is selectively coupled tothe pump 122 with a clutch 34. In other embodiments, the power takeoffunit 32 is directly coupled to the pump 122 (e.g., without clutch 34,etc.). In some embodiments, the concrete mixing truck 10 does notinclude the clutch 34. By way of example, the power takeoff unit 32 maybe directly coupled to the pump 122 (e.g., a direct configuration, anon-clutched configuration, etc.). According to an alternativeembodiment, the power takeoff unit 32 includes the clutch 34 (e.g., ahot shift PTO, etc.). In one embodiment, the clutch 34 includes aplurality of clutch discs. When the clutch 34 is engaged, an actuatorforces the plurality of clutch discs into contact with one another,which couples an output of the transmission 18 with the pump 122. In oneembodiment, the actuator includes a solenoid that is electronicallyactuated according to a clutch control strategy. When the clutch 34 isdisengaged, the pump 122 is not coupled to (i.e., is isolated from) theoutput of the transmission 18. Relative movement between the clutchdiscs or movement between the clutch discs and another component of thepower takeoff unit 32 may be used to decouple the pump 122 from thetransmission 18.

In one embodiment, energy flows along a second power path defined fromthe engine 16, through the transmission 18 and the power takeoff unit32, and into the pump 122 when the clutch 34 is engaged. When the clutch34 is disengaged, energy flows from the engine 16, through thetransmission 18, and into the power takeoff unit 32. The clutch 34selectively couples the pump 122 to the engine 16, according to anexemplary embodiment. In one embodiment, energy along the first flowpath is used to drive the wheels 22 of the concrete mixing truck 10, andenergy along the second flow path is used to operate the drum drivesystem 120 (e.g., power the pump 122, etc.). By way of example, theclutch 34 may be engaged such that energy flows along the second flowpath when the pump 122 is used to provide hydraulic fluid to the drummotor 126. When the pump 122 is not used to drive the mixing drum 102(e.g., when the mixing drum 102 is empty, etc.), the clutch 34 may beselectively disengaged, thereby conserving energy. In embodimentswithout clutch 34, the mixing drum 102 may continue turning (e.g., atlow speed) when empty.

The drum motor 126 is positioned to drive the rotation of the mixingdrum 102. According to an exemplary embodiment, the drum motor 126 is avariable displacement motor. In one embodiment, the drum motor 126operates within a variable speed range up to about 3:1 or 4:1. In otherembodiments, the drum motor 126 is configured to provide a differentspeed range (e.g., greater than 4:1, less than 3:1, etc.). According toan exemplary embodiment, the speed range of the drum drive system 120 isthe product of the speed range of the pump 122 and the speed range ofthe drum motor 126. The drum drive system 120 having the pump 122 andthe drum motor 126 may thereby have a speed range that reaches up to30:1 or 40:1 (e.g., without having to operate the engine 16 at a highidle condition, etc.). According to an exemplary embodiment, increasedspeed range of the drum drive system 120 having a variable displacementmotor and a variable displacement pump relative to a drum drive systemhaving a fixed displacement motor frees up boundary limits for theengine 16, the pump 122, and the drum motor 126. Advantageously, withthe increased capacity of the drum drive system 120, the engine 16 doesnot have to run at either high idle or low idle during the variousoperating modes of the drum assembly 100 (e.g., mixing mode, dischargingmode, filling mode, etc.), but rather the engine 16 may be operated at aspeed that provides the most fuel efficiency and most stable torque.Also, the pump 122 and the drum motor 126 may not have to be operated atdisplacement extremes to meet the speed requirements for the mixing drum102 during various applications, but can rather be modulated to the mostefficient working conditions (e.g., by the drum control system 150,etc.).

As shown in FIG. 2, the drum drive system 120 includes a drivemechanism, shown as drum drive wheel 128, coupled to the mixing drum102. The drum drive wheel 128 may be welded, bolted, or otherwisesecured to the head of the mixing drum 102. The center of the drum drivewheel 128 may be positioned along the axis 104 such that the drum drivewheel 128 rotates about the axis 104. According to an exemplaryembodiment, the drum motor 126 is coupled to the drum drive wheel 128(e.g., with a belt, a chain, a gearing arrangement, etc.) to facilitatedriving the drum drive wheel 128 and thereby rotate the mixing drum 102.The drum drive wheel 128 may be or include a sprocket, a cogged wheel, agrooved wheel, a smooth-sided wheel, a sheave, a pulley, or stillanother member. In other embodiments, the drum drive system 120 does notinclude the drum drive wheel 128. By way of example, the drum drivesystem 120 may include a gearbox that couples the drum motor 126 to themixing drum 102. By way of another example, the drum motor 126 (e.g., anoutput thereof, etc.) may be directly coupled to the mixing drum 102(e.g., along the axis 104, etc.) to rotate the mixing drum 102.

According to an exemplary embodiment, the speed of the mixing drum 102is directly proportional to the speed of the drum motor 126 (e.g., basedon gearing, pulley, etc. arrangement between the drum motor 126 and thedrum drive wheel 128, etc.). The speed of the mixing drum 102 may berepresented by following expression:

$\begin{matrix}{{N_{d} \propto N_{m}} = \frac{Q}{Dsp_{m}}} & (1)\end{matrix}$where N_(d) is the speed of the mixing drum 102, N_(m) is the speed ofthe drum motor 126, Q is the hydraulic fluid flow provided to the drummotor 126 by the pump 122, and Dsp_(m) is the displacement of the drummotor 126. In a drum drive system where the drum actuator is a fixeddisplacement motor, the motor displacement is a constant and the speedof the drum motor 126, and thereby the speed of the mixing drum 102, isbased solely on the hydraulic fluid flow provided by the pump 122.Advantageously, the drum drive system 120 of the present disclosureincludes a variable displacement drum motor 126 such that the speed ofthe mixing drum 102 is based on the hydraulic fluid flow provided by thepump 122 and the displacement of the drum motor 126.

The hydraulic fluid flow provided by the pump 122 to the drum motor 126may be represented by the following expression:Q=N _(p) ·Dsp _(p)  (2)where N_(p) is the speed of the pump 122 and Dsp_(p) is the displacementof the pump 122. Since the pump 122 is driven by the engine 16 with thepower takeoff unit 32, the speed of the pump 122 is proportional to thespeed of the engine 16 (e.g., approximately a 1:1 ratio, etc.), andthereby the hydraulic fluid flow is proportional to the speed of theengine 16. A pump with higher displacement will provide more flow.However, increasing the displacement of a pump increases the size,weight, and cost thereof. Larger pumps also have a much lower allowableworking speed because of the eccentric force from the increase in mass.Typically, the smallest pump to meet the work requirement is selectedand the engine is typically operated at the high idle when high drumspeed is needed. However, this leads to various disadvantageous suchunnecessary fuel consumption, more emissions, increased noise, reducedengine life, etc. The drum motor 126 having variable displacementalleviates the aforementioned disadvantages of a drum drive systemhaving a fixed displacement motor.

According to an exemplary embodiment, the drum motor 126 has a torquecapacity that is capable of meeting the most severe work loadexperienced by the drum assembly 100. The torque capacity of the drummotor 126 may be represented by the following expression:T _(m) =Dsp _(m) ·P _(Q)  (3)where is the torque of the drum motor 126 and P_(Q) is the pressure ofthe hydraulic fluid flow provided to the drum motor 126 by the pump 122.A similar expression may be used to represent the torque capacity of thepump 122. The pump 122 and the drum motor 126 may have a thresholdworking pressure (e.g., 5000 pounds-per-square-inch (“psi”), etc.). Theenergy required to operate the mixing drum 102 at a certain speed may berepresented by the following expression:HP=N _(m) ·T _(m) =P _(Q) ·Q  (4)where HP is the horsepower of the drum drive system 120.

The most severe workloads appear when the mixing drum 102 is inacceleration, braking, and/or discharging (e.g., where the speed of themixing drum 102 is in low to medium range, etc.). In a loading mode or amixing mode, the speed of the mixing drum 102 is high but stable. Thetorque required for the loading and mixing modes is typically less thanhalf of the most severe loads. During low speed and high torqueconditions, the drum motor 126 may be configured to operate in a largedisplacement setting to provide the required torque. In a high speed butrelative stable torque condition, the drum motor 126 may be configuredto operate at a reduced displacement so as to require less flow for thesame rotating speed. Then, the speed of the pump 122, and thereby thespeed of the engine 16 may be reduced.

By way of example, during an initial stage of operation, the drum motor126 may be operated at 100% displacement and the system pressure may beat 2000 psi. The pump 122 may also be operated at 100% displacement. Theengine may be operated at a high idle speed of 2000 rpm. Now, if thedisplacement of the drum motor 126 is reduced to 50% of the maximumamount of displacement, only half of the original hydraulic flow isneeded to maintain the same motor speed, based on Equation (1). However,because the mixing drum 102 is still running with the same load at thesame speed, the horsepower consumption will not change. From Equation(4), the system pressure will double with the same horsepowerconsumption and half the hydraulic fluid flow. Therefore, the systempressure will increase to 4000 psi from the original 2000 psi. Further,now that half of the original amount of hydraulic fluid flow isrequired, the pump 122 may be operated at half of the original speedthereof with the full displacement setting, based on Equation (2). As aresult, the engine 16 may be operated at half of the high idle speed(e.g., 1000 rpm instead of 2000 rpm, etc.) since the speed of the pump122 is proportional to the speed of the engine 16. Therefore, the drumdrive system 120 is capable of providing the same horsepower outputwhile at significantly lower engine speeds, which provides much betterfuel efficiency, less emissions, decreased operational noise, increasedengine life, etc.

By way of another example, concretes may not always be low slump heavymaterials. With high slump light concrete, the drum work load can bemuch lighter. The system pressure may only be at 1500 psi with the drummotor 126 at full displacement. The motor displacement can be furtherdecreased to less than 50%, for example 40%. The system pressure mayonly be 3750 psi (e.g., which is less than the maximum allowable systempressure, etc.). Then, the engine 16 may be operated at a low idle speed(e.g., 800 rpm, etc.).

According to the exemplary embodiment shown in FIG. 3, the drum controlsystem 150 for the drum assembly 100 of the concrete mixing truck 10includes a controller, shown as drum assembly controller 152. In oneembodiment, the drum assembly controller 152 is configured toselectively engage, selectively disengage, control, and/or otherwisecommunicate with components of the drum assembly 100 and/or the concretemixing truck 10 (e.g., actively control the components thereof, etc.).As shown in FIG. 3, the drum assembly controller 152 is coupled to theengine 16, the pump 122, the drum motor 126, a first pressure sensor154, a second pressure sensor 156, and a speed sensor 158. The pump 122is coupled to the engine 16 (e.g., by way of a PTO connection on atransmission of the concrete mixing truck 10, etc.). In otherembodiments, the drum assembly controller 152 is coupled to more orfewer components. The drum assembly controller 152 may be configured toregulate the speed of the engine 16, the displacement of the pump 122,and/or the displacement of the drum motor 126 to provide a target speed(e.g., received from an operator, etc.) of the mixing drum 102. By wayof example, the drum assembly controller 152 may send and receivesignals with the engine 16, the pump 122, the drum motor 126, the firstpressure sensor 154, the second pressure sensor 156, and/or the speedsensor 158.

The drum assembly controller 152 may be implemented as hydrauliccontrols, a general-purpose processor, an application specificintegrated circuit (ASIC), one or more field programmable gate arrays(FPGAs), a digital-signal-processor (DSP), circuits containing one ormore processing components, circuitry for supporting a microprocessor, agroup of processing components, or other suitable electronic processingcomponents. According to an exemplary embodiment, the drum assemblycontroller 152 includes a processing circuit having a processor and amemory. The processing circuit may include an ASIC, one or more FPGAs, aDSP, circuits containing one or more processing components, circuitryfor supporting a microprocessor, a group of processing components, orother suitable electronic processing components. In some embodiments,the processor is configured to execute computer code stored in thememory to facilitate the activities described herein. The memory may beany volatile or non-volatile computer-readable storage medium capable ofstoring data or computer code relating to the activities describedherein. According to an exemplary embodiment, the memory includescomputer code modules (e.g., executable code, object code, source code,script code, machine code, etc.) configured for execution by theprocessor.

According to an exemplary embodiment, the drum assembly controller 152is configured to regulate the engine speed, the pump displacement, andthe motor displacement to provide a target drum speed, while maintainingthe engine speed at a lowest possible level while using pump and motordisplacement changes to achieve the target hydraulic fluid flow andhydraulic power demand. The control of the drum speed can be achieved byusing a target drum speed error to calculate the pump and motordisplacement changes with minor or no changes to the engine speedthrough a proportional-integral-derivative (“PID”) based controlstrategy. A look-up table based or gain-scheduling, or other forms ofcontrol strategies can also be used to adjust the pump and motordisplacement independently. In some embodiments, the drum assemblycontroller 152 is configured to operate the engine 16 at the lowestpossible engine speed, the pump 122 at the lowest possible pumpdisplacement, and the drum motor 126 at the highest possible motordisplacement to achieve the target drum speed within constraints such asmaximum hydraulic pressure, maximum engine torque/load, and maximum drumspeed. To facilitate such control, the drum control system is configuredto monitor (i) the working pressure of the hydraulic fluid flow on bothsides of the drum motor 126 and the pump 122 with the first pressuresensor 154 and the second pressure sensor 156, (ii) the speed of thedrum motor 126 with the speed sensor 158 (i.e., which is proportional tothe speed of the mixing drum 102), (iii) the speed of the engine 16,(iv) the torque of the engine 16, and/or (v) a percent load on the drumdrive system 120. Further details regarding a control strategyimplemented by the drum assembly controller 152 are provided herein inrelation to method 500. In other embodiments, the drum control system150 does not employ pressure feedback control (e.g., employs open loopcontrol, controls based on other feedbacks, hydraulic components withhigher pressure operating conditions are employed, etc.). In still otherembodiments, the drum control system 150 is configured to adjust thedisplacement of the drum motor 126 in response to at least one of (i) atorque of the engine 16, (ii) a load on the engine 16, and (iii) a powerof the engine 16. In yet other embodiments, the drum control system isconfigured to adjust the displacement of the drum motor 126 in responseto at least one of (i) a torque of the engine 16 and (ii) a torque ofthe pump 122 and a displacement of the pump 122.

Referring now to FIG. 5, a method 500 for controlling a drum drivesystem having a variable displacement pump and a variable displacementmotor to provide a target drum speed by modulating engine speed, pumpdisplacement, and motor displacement, is shown according to an exemplaryembodiment. The method may include maintaining the engine speed at thelowest required level while actively controlling pump displacement andmotor displacement to provide the required power demand to operate thedrum at the target drum speed.

At step 502, a control system (e.g., the drum control system 150, thedrum assembly controller 152, etc.) is configured to receive and monitorpressure data indicative of a system pressure (e.g., pressure of thehydraulic fluid flow, etc.) within a drum drive system (e.g., the drumdrive system 120, etc.) from at least one pressure sensor (e.g., thefirst pressure sensor 154, the second pressure sensor 156, etc.). Atstep 504, the control system is configured to determine whether thesystem pressure is less than a maximum or threshold pressure (e.g., 5000psi, etc.) for the drum drive system. If the system pressure is lessthan the maximum or threshold pressure (e.g., by more than a thresholddifference, etc.), the control system is configured to proceed to step506.

At step 506, the control system is configured to reduce a displacementof a variable displacement motor (e.g., the drum motor 126, etc.) of thedrum drive system in response to the system pressure being less than themaximum or threshold pressure. At step 508, the control system isconfigured to reduce a speed of an engine (e.g., the engine 16, etc.)coupled to a pump (e.g., the pump 122, etc.) of the drum drive systembased on the reduction in displacement of the variable displacementmotor (e.g., if the speed of the engine is not at idle, unless thetransmission of the vehicle is in drive and is then independentlycontrolled based on vehicle driving needs, etc.). The control system maythen return to step 502 to further reduce the speed of the engine, ifpossible. If the system pressure is not less than a maximum or thresholdpressure (e.g., 5,000 psi, etc.) for the drum drive system, the controlsystem is configured to determine, at step 510, whether the systempressure is at or near the maximum or threshold pressure for the drumdrive system. If the system pressure is at or near the maximum orthreshold pressure for the drum drive system, the control system isconfigured to increase a displacement of a variable displacement motorof the drum drive system at step 512 and increase a speed of an enginecoupled to a pump of the drum drive system based on the increase indisplacement of the variable displacement motor at step 514 andthereafter return to step 502.

According to an exemplary embodiment, reducing the displacement of thevariable displacement motor will generate a higher system pressure. Byway of example, reducing the displacement of the variable displacementmotor requires less fluid flow to maintain the same speed of thevariable displacement motor, and thereby maintain the speed of the drum(e.g., see Equation (1), etc.). However, because the drum needs tocontinue running with the same load at the same speed, the horsepowerconsumption to drive the drum does not change. With the same horsepowerconsumption and a reduced fluid flow, the system pressure will increase(e.g., see Equation (4), etc.). With the fluid flow reduced, the pumpmay be operated by the control system at a reduced speed whilemaintaining the current displacement setting thereof (e.g., see Equation(2), etc.). Since the speed of the pump is proportional to the speed ofthe engine, the control system may operate the engine at a reducedspeed. Therefore, control system is configured to control the engine,the pump, and the motor to provide the same horsepower output and drumspeed while at significantly lower engine speeds, which may provideincreased fuel efficiency, reduced emissions, decreased operationalnoise, increased engine life, etc.

In still another embodiment, the pump displacement, the motordisplacement, and the engine speed are controlled as shown in FIG. 6.FIG. 7 shows one exemplary traditional control scheme for comparisonpurposes. According to one embodiment, an increasing drum speed command(e.g., for a drum drive system having a fixed displacement motor, etc.)for one or more target drum speeds, for a decreasing drive ratio, etc.)includes several stages of control: (i) the pump displacement isincreased and/or set to achieve a target drum speed at a current enginespeed (e.g., a speed that may be uncontrolled such as when driving,etc.) and maximum motor displacement, (ii) the variable motordisplacement is decreased to achieve the target drum speed at themaximum pump displacement and the current engine speed, and (iii)increase engine speed to achieve the target drum speed at maximum pumpdisplacement and a minimum motor displacement. The third control statemay be executed only when possible (e.g., the vehicle is not driving,the transmission 18 thereof is in neutral such that the vehicle drivesystem 20 is not being driven, etc.). As shown in FIGS. 6 and 7, thegraphs 600 and 700 include exemplary plots for (i) the relationshipbetween pump displacement versus drum speed (610 and 710), (ii) therelationship between motor displacement versus drum speed (620 and 720),and (iii) the relationship between engine speed versus drum speed (630and 730). The minimum motor displacement may be limited (e.g., duringthe second stage of control, etc.) based on at least one of a targethydraulic pressure (e.g., differential, gauge, absolute, etc.), amaximum hydraulic pressure engine load, engine torque, pump torque,motor torque, etc. The minimum motor displacement may additionally oralternatively be limited based on a mechanical or software lowerthreshold. The engine speed may be limited (e.g., during the third stageof control, etc.) based on at least one of engine load, engine torque,pump torque, motor torque, hydraulic pressure, etc. Engine speed controlmay be employed after motor displacement control and pump displacementcontrol have been utilized. The motor displacement may be kept as highas possible until necessary for speed control (e.g., and improvecomponent durability, etc.). The order of control used to achieve agiven speed may include, by way of example, increasing pump displacementuntil it is at a maximum, then decreasing motor displacement until it isat the minimum threshold (e.g., acceptable, etc.) level, and thereafterincreasing engine speed until the target drum speed is achieved.

The control system of the present disclosure may address threeconstraints that could otherwise impact performance (e.g., reduce orprevent the ability to achieve or maintain the desired combination motordisplacement, pump displacement, and engine speed, etc.). By way ofexample, engine speed may be controllable only when the vehicle is notbeing driven (e.g., the transmission of the vehicle is in a neutralgear, etc.). By way of another example, the engine may not be configuredto provide the required power at a low speed (e.g., a low idle speed,the lowest possible speed, the lowest desired speed, etc.). By way ofyet another example, the hydraulic system may be configured to operatebelow a threshold pressure (e.g., to maintain component durability,etc.). The control system of the present disclosure may monitor enginepower by evaluating percent load. In response to the engine percentloading exceeding a threshold level (e.g., 80%, etc.), the controllermay be configured to increase engine speed and increase motordisplacement to provide a desired drum speed (e.g., to prevent theengine from stalling, etc.). The controller may be configured topreemptively increase the engine speed for elevated drum speeds (e.g.,reducing or limiting the prevalence of system “hunting” of engine speed,which may be much more noticeable than valve hunting due to engine noisechanges). The control system of the present disclosure may monitorhydraulic pressure (e.g., differential, gauge, absolute, maximum, etc.).In one embodiment, the controller is configured to lower the pressure inresponse to the pressure exceeding a threshold level (e.g., 4,500 psi,etc.) by increasing motor displacement and increasing engine speed tomaintain the desired drum speed. The controller may be configured topreemptively increase the engine speed for elevated drum speeds (e.g.,reducing or limiting the prevalence of system “hunting” of engine speed,which may be much more noticeable than valve hunting due to engine noisechanges).

The present disclosure contemplates methods, systems and programproducts on memory or other machine-readable media for accomplishingvarious operations. The embodiments of the present disclosure may beimplemented using existing computer processors, or by a special purposecomputer processor for an appropriate system, incorporated for this oranother purpose, or by a hardwired system. Embodiments within the scopeof the present disclosure include program products or memory comprisingmachine-readable media for carrying or having machine-executableinstructions or data structures stored thereon. Such machine-readablemedia can be any available media that can be accessed by a generalpurpose or special purpose computer or other machine with a processor.By way of example, such machine-readable media can comprise RAM, ROM,EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to carry or store desired program code in the form ofmachine-executable instructions or data structures and which can beaccessed by a general purpose or special purpose computer or othermachine with a processor. Combinations of the above are also includedwithin the scope of machine-readable media. Machine-executableinstructions include, by way of example, instructions and data whichcause a general purpose computer, special purpose computer, or specialpurpose processing machines to perform a certain function or group offunctions.

As utilized herein, the terms “approximately”, “about”, “substantially”,and similar terms are intended to have a broad meaning in harmony withthe common and accepted usage by those of ordinary skill in the art towhich the subject matter of this disclosure pertains. It should beunderstood by those of skill in the art who review this disclosure thatthese terms are intended to allow a description of certain featuresdescribed and claimed without restricting the scope of these features tothe precise numerical ranges provided. Accordingly, these terms shouldbe interpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimedare considered to be within the scope of the invention as recited in theappended claims.

It should be noted that the term “exemplary” as used herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” “connected,” and the like, as used herein, mean thejoining of two members directly or indirectly to one another. Suchjoining may be stationary (e.g., permanent) or moveable (e.g.,removable, releasable, etc.). Such joining may be achieved with the twomembers or the two members and any additional intermediate members beingintegrally formed as a single unitary body with one another or with thetwo members or the two members and any additional intermediate membersbeing attached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,”“above,” “below,” etc.) are merely used to describe the orientation ofvarious elements in the figures. It should be noted that the orientationof various elements may differ according to other exemplary embodiments,and that such variations are intended to be encompassed by the presentdisclosure.

Also, the term “or” is used in its inclusive sense (and not in itsexclusive sense) so that when used, for example, to connect a list ofelements, the term “or” means one, some, or all of the elements in thelist. Conjunctive language such as the phrase “at least one of X, Y, andZ,” unless specifically stated otherwise, is otherwise understood withthe context as used in general to convey that an item, term, etc. may beeither X, Y, Z, X and Y, X and Z, Y and Z, or X, Y, and Z (i.e., anycombination of X, Y, and Z). Thus, such conjunctive language is notgenerally intended to imply that certain embodiments require at leastone of X, at least one of Y, and at least one of Z to each be present,unless otherwise indicated.

It is important to note that the construction and arrangement of theelements of the systems and methods as shown in the exemplaryembodiments are illustrative only. Although only a few embodiments ofthe present disclosure have been described in detail, those skilled inthe art who review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements. It should be noted that the elements and/or assemblies ofthe components described herein may be constructed from any of a widevariety of materials that provide sufficient strength or durability, inany of a wide variety of colors, textures, and combinations.Accordingly, all such modifications are intended to be included withinthe scope of the present inventions. Other substitutions, modifications,changes, and omissions may be made in the design, operating conditions,and arrangement of the preferred and other exemplary embodiments withoutdeparting from scope of the present disclosure or from the spirit of theappended claims.

The invention claimed is:
 1. A vehicle comprising: an engine; atransmission coupled to the engine; a drum configured to mix drumcontents received therein; a drum drive system coupled to the drum andthe engine, the drum drive system including: a pump mechanically coupledto the engine such that a pump speed of the pump is based on a speed ofthe engine, the pump configured to pump a fluid through a hydraulicsystem, the pump having a variable pump displacement; and a motorfluidly coupled to the pump by the hydraulic system such that a motorspeed of the motor is based on a flow of the fluid received from thepump, the motor positioned to drive the drum to agitate the drumcontents, the motor having a variable motor displacement; a pressuresensor positioned along the hydraulic system between the pump and themotor to acquire pressure data indicative of a pressure of the fluidwithin the hydraulic system; and a control system coupled to thepressure sensor, the engine, and the drum drive system, the controlsystem configured to: operate the engine, the motor, and the pump todrive the drum; receive the pressure data from the pressure sensor; andin response to the pressure of the fluid being below a thresholdpressure and the transmission being in neutral, and while maintaining aspeed of the drum: reduce the variable motor displacement of the motorreduce the speed of the engine, which thereby decreases the pump speedof the pump; and increase the variable pump displacement of the pump. 2.The vehicle of claim 1, wherein the control system is configured tomanipulate the speed of the engine while the transmission of the vehicleis in neutral, and wherein the control system is configured to permitthe speed of the engine to vary independent of the speed of the drumwhile the transmission of the vehicle is not in neutral.
 3. The vehicleof claim 1, wherein the drum drive system is capable of providing anoverall drive ratio between 30:1 and 40:1, the overall drive ratio beinga product of a pump speed range of the pump and a motor speed range ofthe motor, the pump speed range being a ratio of a maximum pumpdisplacement to a minimum pump displacement of the pump, and the motorspeed range being a ratio of a maximum motor displacement to a minimummotor displacement of the motor.
 4. The vehicle of claim 3, wherein thepump has the pump speed range of about 10:1.
 5. The vehicle of claim 4,wherein the motor has the motor speed range of about 3:1.
 6. The vehicleof claim 4, wherein the motor has the motor speed range of about 4:1. 7.The vehicle of claim 1, wherein the control system is configured to:increase the variable motor displacement of the motor in response to thepressure of the fluid being at or greater than the threshold systempressure; and increase the speed of the engine based on the increase inthe variable motor displacement, while maintaining the speed for thedrum.
 8. The vehicle of claim 1, wherein the control system isconfigured to maintain the speed of the engine and not decrease thespeed of the engine if at an idle speed of the engine.
 9. The vehicle ofclaim 1, wherein the control system is configured to control the speedof the engine independent of the speed of the drum while maintaining thespeed of the drum if the transmission is in gear and the engine isdriving the vehicle.
 10. The vehicle of claim 1, wherein the controlsystem is configured to initially operate (i) the motor at a maximummotor displacement and (ii) the engine and the pump at a lowest possibleengine speed and a lowest possible pump displacement, respectively, thatachieves the speed of the drum.
 11. The vehicle of claim 1, wherein, inresponse to the pressure of the fluid being at or above the thresholdpressure and the transmission being in neutral, and while maintainingthe speed of the drum, the control system is configured to: increase thespeed of the engine, which thereby increases the pump speed of the pump;decrease the variable pump displacement of the pump; and increase thevariable motor displacement of the motor.
 12. The vehicle of claim 1,wherein the control system is configured to increase the speed of theengine in response to (i) the variable pump displacement reaching amaximum pump displacement of the pump and (ii) the variable motordisplacement reaching a minimum motor displacement of the motor toachieve an increased speed.
 13. A vehicle comprising: an engine; amixing drum; a drum drive system including: a variable displacement pumpselectively mechanically couplable to the engine such that a pump speedof the variable displacement pump is based on an engine speed of theengine; and a variable displacement motor fluidly coupled to thevariable displacement pump such that a motor speed of the variabledisplacement motor is based on a flow of a fluid received from thevariable displacement pump, wherein the variable displacement motor isconfigured to drive the mixing drum at a target drum speed; and acontroller configured to selectively control the engine, the variabledisplacement pump, and the variable displacement motor to provide thetarget drum speed, wherein the target drum speed is based on an inputfrom an operator of the vehicle, and wherein to provide the target drumspeed, the controller is configured to: (i) initially operate thevariable displacement motor at a maximum motor displacement and operatethe variable displacement pump at a pump displacement that provides thetarget drum speed without needing to actively manipulate the enginespeed; (ii) increase the pump displacement and decrease a motordisplacement without needing to actively manipulate the engine speedwhile still providing the target drum speed; and (iii) increase theengine speed in response to the pump displacement reaching a maximumpump displacement and the motor displacement reaching a minimum motordisplacement if necessary to maintain the target drum speed.
 14. Thevehicle of claim 13, wherein the drum drive system is capable ofproviding an overall drive ratio between 30:1 and 40:1, the overalldrive ratio being a product of a pump speed range of the variabledisplacement pump and a motor speed range of the variable displacementmotor, the pump speed range being a ratio of the maximum pumpdisplacement to a minimum pump displacement of the variable displacementpump, and the motor speed range being a ratio of the maximum motordisplacement to the minimum motor displacement of the variabledisplacement motor.
 15. The vehicle of claim 14, wherein the variabledisplacement pump has the pump speed range of 10:1.
 16. The vehicle ofclaim 15, wherein the variable displacement motor has the motor speedrange of 3:1 or 4:1.
 17. The vehicle of claim 13, further comprising atransmission, wherein the engine speed can be actively manipulated ifthe transmission is in neutral.
 18. The vehicle of claim 13, furthercomprising a transmission, wherein the engine speed is increased if thetransmission is in neutral.